Constant potential transformer



J. G, SOLA Jan. 10, 1939.

CONSTANT POTENT IAL TRANSFORMER Filed Aug. 31, 1938 2 heeisSheet l Jan.10, 1939; J. G. SOLA 2,143,745

CONSTANT POTENTIAL TRANSFORMER Filed Au 31, 1938 2 Sheets-Sheet 2Patented Jan. 10, 1939 PATENT OFFICE CONSTANT ro'rsn'rmr. TRANSFORMERJoseph G. Sola, Oak Park, IlL, assignor to Sola Electric 00., Chicago,11]., a corporation of Delaware Application August 31, 1938, Serial No.227,626

12 Claims.

' My invention relates to an improved constant potential transformer bymeans of which variations of input voltage over a wide range of limitsmay take place without affecting the output voltage to any substantialextent.

One of the objects of my invention is to provide a constant potentialtransformer which is compact as a unit and which may be economicallymanufactured. in It is another object of my invention to provide atransformer of this type in which the emciency and input power factorare high while the temperature rise of the magnetic core is low.

A further object of my invention is to provide if) a transformer, theoutputvoltage wave of which will have very little distortion and thedevice will be satisfactory for various commercial-applications.

The invention consists of the novel construc- 20 tions, arrangments anddevices to be hereinafter described and claimed for carrying out theabove stated objects and such other objects as will appear from thefollowing description of certain preferred embodiments illustrated inthe accompanying drawings, wherein,-

Fig. 1 is a sectional view of one form of construction that may be used;

Fig. 2 is a diagrammatic illustration of the wiring arrangement that maybe used in connec- 30 tion with a construction such as that shown inFig. 1;

Fig. 3 is a sectional view of another form of construction embodying theprinciples of my invention;

35 Fig. 4 is a diagrammatic illustration of the wiring arrangement thatmay be used in connection with a construction such as that shown in Fig.3;

, Fig. 5 is a diagram showing the vector relations 40 between thevarious voltages obtained in the illustrated constructions at differentvalues of input voltage; and

Fig. 6 is a graph showing the relation between the magnitudes of variousvoltages obtained in 45 the illustrated constructions as the inputvoltage is varied.

Like characters of reference designate like parts in the several views.

Referring to Figs. 1 and 2, it will be seen that 50 a core type oftransformer construction is illustrated, the closed magnetic circuit IDof which comprises a stack of I-shaped laminations II in abuttingrelation with the end legs l2a of a stack of E-shaped laminations l2,which may be held 5 together by any suitable means. On the end portion Aof the core bar H, I have provided a primary winding I3, the terminalsI4 and I of which are adapted to be connected with a source ofalternating current, the voltage of which from 7 time to time mayfluctuate or vary substantially. 5

On the end portion B of the core bar H, I have mounted a winding it,which is in spaced relation to but magnetically coupled with the winding13, the winding is having terminal leads I1 and I8 and an intermediatetap l9. That part 10 of the winding IE between the lead l1 and tap l9may be considered as an output or load winding, and the entire windingl6 between the leads I1 and I8 may be termed an intermediate winding.The magnetic core III is provided with a high leakage reactance pathbetween the windings l3 and it which in the form shown comprises thecentral leg l2b of the E-shaped laminations and which terminates shortof the core bar I l thereby providing a non-magnetic or air gap between20 said leg l2b and the core bar I I. In this arrangement, a condenser2| is connected by leads 22 across the terminals I1 and 18 of thewinding IS. The lead II forms one side and the tap IS the other side ofwhat may be termed an output or load circuit. In the arrangement shown,an auxiliary winding 23 is positioned over the winding 13 and ismagnetically coupled therewith, the terminals 24 of said winding 23being connected in series in the lead IQ of said output circuit.

In Figs. 3 and 4, I have illustrated my invention in connection with awell-known shell type of transformer having two closed magnetic circuitsIll and la comprising a straight central core bar 25 of I-shapedlaminations, the sides of which are in abutting contact with the endlegs 26a of the E-shaped laminations 26 and the end legs 21a of theE-shaped laminations 21, said parts being held in operative relation byany suitable means. On the end portion A, of the core 0 bar 25, I havemounted a primary winding 28 the terminals 29 and 30 of which areadapted to be connected to a source of alternating current, the voltageof which may fluctuate substantially from time to time. Another winding3| is positioned on the end portion B of the core bar 25, the winding 3|being in spaced relation to but magnetically coupled loosely with thewinding 28. A condenser 32 is connected across the terminals 33 and 34of the winding 3i. Another winding 35 is mounted on the end portion B ofthe core bar 25, in the arrangement shown the winding 35 beingpositioned over and magnetically coupled tightly with the winding 3|.The terminal 36 of the winding 35 leads to one side of what may 5 betermed an output circuit. An auxiliary winding 31 is positioned on theend portion A of the core bar 28 and in the arrangement illustrated thewinding 31 is positioned over and magnetically coupled tightly with thewinding 28. A lead 38 connects the winding .31 in series with thewinding 35, the lead 39 of the winding 31 forming the other side of theaforesaid output circuit. The winding 35 may be termed an output or loadwinding and the winding 3| may be considered as an intermediate winding.The closed magnetic circuits described are each provided with a highleakage reactance path between the windings 28 and 31 on the end portionA of the core bar 25 and the windings 3| and 35 on the end portion B ofsaid core bar, which in the arrangement shown comprise the central legsand 4| 0! the respective E laminations 28 and 21. The shunts 40 and 4|terminate short of the adjacent sides of the core bar 25 therebyproviding non-magnetic or air gaps 42 and 43 between the legs 40 and 4|and the core bar 25.

In Figs. 2, 4, 5 and 6 V0 represents the voltage across the outputcucumv, shows the input voltage on the primary winding, V; indicates thevoltage derived from the winding l8 between the lead l1 and tap l3,'andfrom the winding 35 forming parts of the respective output circuits, andVpa is the component 0! the output voltage taken across the terminals ofthe auxiliary winding 23 or 31, as the case may be.

In Fig. 5, I have shown the vector relations of the various voltages ineither arrangement at a certain power output and at diflerent values ofprimary voltage. The various voltages are either not primed or areprimed to correspond to the difierent values of V, which is varied. Asshown, V is nearly 180 out of phase with V, and hence the vectorial sumV0 of the two is approximately their numerical diflference.

In Fig. 6, I have illustrated graphically the relation in theconstructions described between V5, V0, Vpa and V atma certain poweroutput.

The principles upon which my improved transformer constructions operatewill be clear from a detailed consideration of the construction shown inFigs. 3 and 4. The flux set up by applying a potential across theprimary winding 28 will link with winding 3| and cause a definitereactance to be set up by that winding. As the voltage on the. primarywinding is increased from zero to a higher level, the flux threadingthrough winding 3| tends to increase in nearly direct proportion totheprlmary flux, due to the reluctance caused by the air gaps 42 and 43,a very slight amount leaking through the shunts 48 and 4|. As theinduced E. M. F. reaches a higher value in winding 3| a critical pointis reached where resonance takes place, since the reactance of theefl'ective inductance of the winding 3| and the capacity reactance ofthe condenser 32 are approximately equal at the frequency of the voltageimpressed on the winding 28, that is to say,

where f is the frequency of the voltage impressed on the primary winding28, L is the effective inductance of the winding 3|, and C is thecapacity of the condenser 32. Under this resonant condition, a definiteamount of current will fiow in the resonant circuit, comprising thewinding 3|, condenser 32 and leads 33 and 34, and such current will belimited by the constants 01' that circuit, with the result that apotential will be set up across the winding 3! and a correspondingamount of magnetic flux will be set up in the end portion B of the corebar 25.

It is well known that the inherent characteristic of a resonant circuitis such that its power vector may be many times greater than that of thegenerator which supplies the energy to the resonant circuit; in thiscase the energy is supplied by the primary oi the transformer to theresonant circuit comprising winding 3| and condenser 32. By varying theprimary voltage across winding 28 so that the magnetic density ofsection A thereof will still remain under the maximum magnetic densityof section B of the core, with which the resonant circuit is associated,the change of flux density in section A of the core due to linevariation in the primary will have no appreciable effect on the resonantcircuit as the reluctance of the leakage path will be under that ofsection B of the core and flux will leak through the leakage pathbetween the primary and resonant core portions, which leakage pathcomprises the shunts 40 and 4| and their respective nonmagnetic gapportions 42 and 43.

It is due to this leakage reactance path also that the co-efiicient ofcoupling between the primary winding 28 and the aforesaid resonantcir-'- cuit is reduced to a certain optimum value, thereby maintaining abalanced condition so that the resonant circuit will continue tooscillate with the maximum current therein at a frequency equal to thefrequency impressed on the primary winding. Under this state ofresonance, winding 3| will set up a magnetic field in the core portion Bwhich will remain practically constant so long as the density in themagnetic field of the core portion A remains at a lower density thanthat of the core portion B. It follows that this substantially constantfield strength in core portion B will produce also a substantiallyconstant voltage across the terminals of winding 3| and condenser 32,and this voltage will remain at practically a constant level regardlessof variation of voltage applied to the primary winding 28.

The aforesaid resonant circuit, therefore, becomes a constant primarysource of voltage for any winding such as the winding 35 that isdirectly coupled to the winding 3|. This coupling can be effected in anydesired way, for example, by means of an auto-type transformerarrangement as shown in Fig. 2, or by mounting the winding 35 over thewinding 3| as shown in Fig. 4. In the Fig. 4 construction, the outputvoltage of the windings 35 will also have a practically constant levelvoltage independent of the voltage variation in the primary winding 28so long as the circuit which includes the winding 3| remains inresonance.

The auxiliary regulating winding 31 is coupled to the portion A of thecore and is used to change the percentage of regulation of V0 across theterminals 36 and 39 of the output circuit with a variation of V Sincethis auxiliary winding 31 on core portion A is directly coupled to theprimary winding 28, the voltage induced will always be proportional tothe turns ratio of primary winding 28 and the auxiliary winding 31.

A very constant level of voltage V. across the terminals 36 and 39 maybe obtained by suitably apportioning the number of turns of saidauxiliary winding 31 in relation to the number of turns in the winding35. Any percentage of regulation of output voltage in relation tovaria-. tions of V9 also may be obtained from terminals 36 and 89,-forexample, an increase in the primary voltage on winding 28 will produce adecrease in output voltage V by properly arranging or apportioningwinding 31 in relation to the winding 35.

The relation of voltages described has been upon the assumption that thetransformer is on an open output circuit, that is to say, with no loadon the terminals 36 and 39. If a load be applied on said terminals,.amagnetic fiux in the aforesaid resonant circuit will be developedcorresponding to the load on said output circuit thereby unbalancing themagnetic fiux in section B of the core. This density change in coresection B will in turn affect the stable relation of the flux in coresections A and B and also the leakage reactance through the aforesaidshunt paths thereby causing a greater amount of useful flux from coresection A to thread through core section B, which compensates for theenergy used by the consuming circuit and at the same time maintains theresonant circuit in the desired oscillating condition.

It will be readily understood that in transformers embodying theprinciples of my invention the primary' winding electrically connectedto the source serves to induce voltage to the resonant circuit which isseparated from the primary circuit by a high leakage reactance path,thereby providing a low co-eflicient of coupling between the primary andthe resonant circuits. The aforesaid resonant circuit may be consideredas the primary or main source of controlling energy to the winding 35and hence'to the output or consuming circuit of the transformer. I

My improved constant potential transformers are compact and efiicient,and are of a small size relative to their power output as compared withother and more cumbersome and expensive apparatus intended for the samepurpose. My improved transformers operate at an inherent high powerfactor, and the output voltage is very close to a pure sine wave.

My improved transformers may be used for many diflerent purposes. Theyare particularly advantageous in connection with commercial applicationssuch as amplifiers for talking motion pictures, amplifiers for radiotransmitters, mercury arc lamps, X-ray apparatus, etc.

I wish it to be understood that my invention is not to be limited to thespecific constructions shown and described, except so far as the claimsmay be so limited, as it will be apparent to those skilled in the artthat changes in the constructions and arrangements may be made withoutdeparting from the principles of my invention.

I claim:

1. In a constant potential transformer, the combination of a magneticcore, a winding on said core adapted to be connected to a source ofalternating current of fluctuating voltage, a second winding on saidcore, said core providing a high leakage reactance path for a portion ofthe fiux to thread through one of the windings to the exclusion of theother winding, and means for maintaining the potential across the secondwinding substantially constant regardless of fluctuations in the inputvoltage comprising a resonant circuit including said second winding anda condenser, the resonant circuit operating at a frequency equal to thefrequency of the voltage impressed on the first winding.

2. In .a. constant potential transformer, the combination of a magneticcore, a winding on said core adapted to be connected to a source ofalternating current of fluctuating voltage, a second winding on saidcore in spaced relation to said first winding, said core havingmagnetically disposed between said windings a magnetically permeableshunt with a non-magnetic gap portion, and means for maintaining thepotential across the second winding substantially constant regardless offluctuations in the input voltage comprising a resonant circuitincluding said second winding and a condenser, the resonant circuitoperating at a frequency equal to the frequency of the voltage impressedon the first winding.

3. In a constant potential transformer, the combination of a closedmagnetic circuit comprising first and second core portions, a winding onsaid first core portion adapted to be connected to a source ofalternating current of fluctuating voltage, a second winding on saidsecond core portion, said circuit providing a high leakage reactancepath for a portion of the flux to thread through one of the windings tothe exclusion of the other winding, and means for maintaining thepotential across the second winding substantially constant regardless offluctuations in the input voltage comprising a resonant circuitincluding said second winding and a condenser, the resonant circuitoperating at a frequency equal to the frequency of the voltage impressedon the first winding, the magnetic density at maximum predeterminedinput voltage of the first core portion being less than the maximummagnetic density of the second core portion.

4. In a constant potential transformer, the combination of a closedmagnetic circuit comprising first and second core portions, a winding onsaid first core portion adapted to be connected to a source ofalternating current of fiuctuating voltage, a second winding on saidsecond core portion in spaced relation to said first winding, saidcircuit having magnetically disposed between said windings amagnetically permeable shunt with a non-magnetic gap portion, and meansfor maintaining the potential across the second winding substantiallyconstant regardless of fluctuations in the input voltage comprising aresonant circuit including said second winding and a condenser, theresonant circuit operating at a frequency equal to the frequency of thevoltage impressed on the first winding, the magnetic density at maximumpredetermined input voltage of the first core portion being less thanthe maximum magnetic density of the second core portion.

5. A constant potential transformer comprising in combination a magneticcore, a primary winding on said core adapted to be connected to a sourceof alternating current of fiuctuating voltage, a load winding on saidcore adapted to be connected to an output circuit, said core providing ahigh leakage reactance path for a portion of the flux to thread throughone of the windings to the and means for maintaining the potentialacross the load winding substantially constant regardless offluctuations in the input voltage comprising a resonant circuitincluding a condenser and a third winding, the resonant circuitoperating at a frequency equal to the frequency of the voltage impressedon the primary winding, the third winding being in inductive relation tothe load winding.

6. A constant potential transformer comprising in combination a magneticcore, a primary winding on said core adapted to be connected to aexclusion of the other winding,

source of alternating current of fluctuating voltage, a'loadwinding onsaid core in spaced relation to said primary winding and adapted to beconnected to an'lnput circuit, said core having magnetically disposedbetween said windings a magnetically permeable shunt with a non-magneticgap portion; and means for maintaining the potential across the loadwinding substantially constant regardless of fluctuations in the inputvoltage comprising a resonant circuit including a condenser and a thirdwinding, the resonant circuit operating at a frequency equal to thefrequency of the voltage impressed on the primary winding, the thirdwinding being in inductive regap portion, and means for maintainingthe'potential across the load winding substantially constant regardlessof fluctuations in the input voltage comprising a resonant circuitincluding a condenser and a third winding, the resonant circuitoperating at a frequency equal to the frequency of the voltage impressedupon the primary winding, the third winding being on the second coreportion and in inductive relation to the load winding, the magneticdensity at maximum predetermined input voltage of the first core portionbeing less than the maximum magnetic density of the second core portion.a a

8. A constant potential transformer comprising in combination a magneticcore; a primarywinding on said core adapted to be connected to a sourceof alternating current of fluctuating voltage, a load winding on saidcore adapted to be connected to an output circuit, said core providing ahigh leakage reactance path for a portion of the flux to thread throughone of the windings to the exclusion of the other winding, a resonantcircuit on said first core portion adapted to be connected to a sourceof alternating current of fluctuating voltage, a load winding on saidsecond core portion and adapted to be connected to an output circuit,said core having magnetically disposed between said windings amagnetically permeable shunt with a non-magnetic gap portion, a resonantcircuit including a condenser and a third winding, the resonant circuitoperating at a frequency equal to the frequency of the voltage impressedon the primary winding, the third winding being in inductive relation tothe load winding, and an auxiliary winding'on'said first core portion ininductive relation to the primary winding and in series with the loadwinding, the magnetic density at maximum predetermined input voltage ofsaid first coreportion being less the maximum density of said secondcore portion.

10. A constant potential transformer comprising in combination amagnetic core, a primary winding on said core adapted to be connected toa source of alternating current of fluctuating voltage, a second windingon said core provided with two leads and an intermediate tap, one ofsaid leads and said tap leading to an output circuit, said coreproviding a high leakage reactance path for a portion of the fluxtothread through one of the windings to the exclusion of the otherwinding, and means for maintaining insaid output circuit a substantiallyconstant potential regardless of fluctuations in the input voltagecomprising a resonant circuit including a condenser connected in seriesbetween the leads of said second winding, the resonant circuit operatingat a frequency equal to the frequency of the voltage impressed on theprimary winding.

11. A constant potential trans former comprising in combination amagnetic core; aprimary winding on said core adapted to be connected toa source of alternating current of fluctuating voltage; a second windingon said core provided with two leads and an intermediate tap; said corehaving magnetically disposed between said windings a magneticallypermeable shunt with a taining in said output circuit a substantiallyconstant potential comprising a resonant circuit ineluding a condenserconnected in series between the leads of the second winding, theresonant circuit operating at a frequency equal to the frequency of thevoltage impressed on the primary winding, and an auxiliary winding onsaid core in inductive relation to the primary winding and in serieswith the load winding.

12. A constant potential transformer comprising in combination a closedmagnetic core comprising first and second core portions; a primarywinding on said first core portion adapted to be connected to a sourceof alternating current of fluctuating voltage; a second winding on thesecond core portion and provided with two leads and an intermediate tap;one of said leadsand saidtap leading to an output circuit; said corehaving magnetically disposed between said windings a magneticallypermeable shunt with a non-magnetic gap portion; the maximum density atmaximum predetermined input voltage of said first core portion beingless than the maximum density of said second core portion; and means formaintaining in said output circuit a substantially constant potentialcomprising a resonant circuit ineluding a condenser connected in seriesbetween the leads of the second winding, the resonant circuit operatingat a frequency equal to the frequency of the voltage impressed on theprimary winding, and an auxiliary winding on said core in inductiverelation to the primary winding and in series with the load winding.

JOSEPH G.- SOLA.

